Download vector images and/or save them as vectors instead of bitmaps.
You don't want to exasperate GN Sleep
I've been using eye-friendly, attractive shapes such as circles and triangles as simple, solid color backgrounds. This eliminates most of your problem. I don't use PS.1. Confusing as hell.2. There are better alternatives than paying $2314752354432852873432 for something I'd only use for transparent BGs.I use Pixlr's advanced editor for creating transparent BGs. It's free, browser based, and easy to use.
wat u could do is before u start colouring in sai, colour in the whole (person or object) and leave that layer white.but your probably selecting the areas and colouring it in thats why its leaving white marks cause ur not colouring past the lines. since its on different layers, colour past the line on 1 layer and cover it with the layer ontop. i use PS to finish off my images so u dont really need to use anything else its just u need to make sure its properly colored in sai then it should be fine. or u could select the image in PS if the edges arent messy it should select the image pretty well and just make a black layer under it, (soften the edges if u have to) and then the white patches should be gone. its not really patches its cause its just not colored.
yh thats alot better. next time just colour it in like i said before like: so next time u wont have to u any layer under it or anything. But i also do sometimes miss places like:so in ps i sort that out by merging all layers then having a drop shadow.. that just sorts everything out really.
what i do is for every section (like skin, hair, top.. and so on) i zoom in pretty close and just outline it myself it exactly, with pen tool, i dont select it. and then fill it in after. if u do get those edges where it doesnt fill in it's easy to cover up cause its easily visible. like: and when u fill in:^stuff like that is easily visible. then your edges are smooth and u have everything filled in. just need to keep practicing with your drawing tablet.